Field of the Disclosure
The present disclosure relates to a display device capable of performing a touch sensing, a method of driving the display device, and a driving circuit of the display device.
Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been necessarily adopted to portable information appliances. The touch UI is implemented by forming a touch screen on the screen of a display device. The touch screen may be implemented as a capacitive touch screen. The touch screen having capacitive touch sensors senses changes (i.e., changes in charges of the touch sensor) in a capacitance resulting from an input of a touch driving signal when a user touches (or approaches) the touch sensor with his or her finger or a conductive material, and thus detects a touch input.
In order to increase touch sensitivity of the capacitive touch screen the user feels, it is necessary to increase a touch report rate. This is because coordinates of the touch input are updated using a frequency of the touch report rate in a host system. Thus, a response time of the host system in response to the touch input is proportional to the touch report rate.
In an in-cell touch sensor technology in which touch sensors of a touch screen are embedded in a pixel array of a display panel, the touch report rate is determined based on a display frame rate. The touch report rate indicates a frequency at which coordinate data obtained by sensing all of the touch sensors included in the touch screen is transmitted to an external host system. The display frame rate indicates a frequency at which all of pixels of the display panel are updated to new data. As the touch report rate increases, a time required to update coordinates of a touch input is reduced. Therefore, the touch sensitivity of the touch screen the user feels can be improved, and a touch input trace can be represented in detail.
When there is little change in an input image on the display device, a technology of changing the display frame rate is known to reduce power consumption of the display device. The technology drives a display device in a low-speed driving mode when the display device, that generally operates in a normal driving mode, meets previously determined low-speed driving conditions. The technology is known as a low refresh rate (LRR) technology.
However, because a refresh cycle of pixel data is longer in the low-speed driving mode than in the normal driving mode, a display frame rate in the low-speed driving mode decreases, and a touch report rate in the low-speed driving mode also decrease. With reference to FIGS. 1A and 1B, this is described in detail below. In FIGS. 1A and 1B, a display frame rate in a normal driving mode is 60 Hz, and a display frame rate in a low-speed driving mode is 20 Hz, by way of example.
In an in-cell touch sensor technology, as shown in FIG. 1A, one display frame period may include one display period Td and one touch period Tt. Alternatively, as shown in FIG. 1B, one display frame period may include a plurality of display periods Td and a plurality of touch periods Tt. The display frame period includes only data write frames WF in the normal driving mode and includes data write frames WF and data hold frames HF in the low-speed driving mode. In the display period Td of the data write frame WF, a write operation D (hereinafter, referred to as “data write operation”) of pixel data is performed. In the touch period Tt of the data write frame WF, an operation T (hereinafter, referred to as “touch operation”) driving touch sensors is performed. On the other hand, in the data hold frame HF, both the data write operation D and the touch operation T are not performed. Thus, a touch report rate is less in the low-speed driving mode including the data hold frame HF than in the normal driving mode. A reduction in the touch report rate in the low-speed driving mode may lead to a large reduction in a touch performance including a reduction in a touch response speed, a cut phenomenon of a touch input trace, etc.